In auto racing a driver typically wears a helmet with a visor to protect the drivers eyes. The visor is particularly important when the vehicle has no front windshield. In many forms of auto racing the vehicle operates without the front windshield including the following categories: formula 1, formula atlantic, stock car racing, Indy type races etc. Without the windshield during a race the visor can become covered with dirt and grime. Thus the driver needs some way to keep the visor clean during a race without having to stop to clean his visor and lose precious time. A common practice used in auto racing for at lest the last 10 to 15 years consists of securing several thin flexible plastic visor tear off shields guards over the front of the visor on the drivers helmet. The tear off shield guards have a tab at one end to allow the driver to tear off each successive shield guard during the race, without having to slow down or stop during the race.
Being able to see the surface definition of a race track is extremely important during a race. The driver must be able to identify slippery areas of the track and breaking points in the curves of the track. Braking points are physical features of a race track which a driver will use to assist in turning in a curve, to brake or to perform some other maneuver which requires, or can be enhanced by a friction point. Among the different types of braking points are cracks in the pavement, rough spots or some other physical feature. To maximize the advantage such a feature offers the driver must be able to clearly see the feature each time he approaches it, generally at a very high rate of speed, in order to properly position his vehicle to take maximum advantage of the feature.
In order to enhance visual acuity to better see the surface definition of the race track, up to the present the driver only had the option of wearing specially tinted glasses under his helmet or wearing a visor tinted for the ambient lighting conditions at the start of the race. If it was raining and over cast them a visor or glasses with an amber tint could be used or if it was sunny a visor or glasses with a grey or smoky tint would prove helpful.
However, if lighting conditions changed during the race such as form cloudy to sunny or visa versa the driver lost the advantage which the particular tinted visor or glasses provided and in fact put the wearer at a disadvantage. For instance, a visor with an amber tint while enhancing vision under cloudy or overcast conditions actually obstructs visual acuity under sunny conditions by making the surface of the tack to bright and shiny and thus washing out the distinguishing features. Add to this the fact that in any race time is every thing and either the format of the race does not allow for pit stops during the race, or the luxury of a pit stop at anytime to change your visor without loss of position or time. In addition changing the whole visor on a helmet in itself creates its own problems in that during the hectic minute or two of a pit stop the driver runs the risk of damaging the helmet or not properly making the change. Sometimes it can take up to 20 minutes to properly make the change of a visor with all of the adjustments that have to be made. Also most racing drivers have a special helmet they wear so it is not possible, generally to merely change the helmet.